Anthrax continues to be one of the most commonly identified potential risks for bioterrorism attacks. Over the past four funding years, our group has collected samples from over 800 military personnel vaccinated with Absorbed Vaccine Anthrax (AVA) in collaboration with the Harley project. We were stunned to learn that ess than half of vaccinated individuals have antibodies able to significantly inhibit in vitro macrophage killing by anthrax Lethal Toxin (LT) (a standard measure of in vitro protection), even though most vaccinees make antibodies against protective antigen (PA). We have identified key humoral epitopes of the responses to PA [1] and lethal factor (LF) [2] that correlate with in vitro protection. Select humoral epitope responses able to protect mice from in vivo LT are found. Our ongoing work characterizes key LF epitopes that are produced in approximately 10% of currently vaccinated individuals to identify additional potential immunotherapeutics or ways to improve the vaccine immune response. Preliminary data suggest that CD4* responses against key vaccine components can be identified. We will build on these advances to understand critical reasons why so many individuals apparently have inadequate responses to the current vaccine and to identify those immune responses that are essential for protection. Our team will build on key humoral epitopes already identified and use our extensive expertise in protein chemistry, epitope mapping and confirmation, molecular modeling, animal immunization, and T cell immunology to identify the common B cell targets of edema factor (EF) and test combinations of peptide epitopes for protection in vivo and in vitro. Previously collected samples from over 800 individuals will allow us to examine Bacillus anthracis T cell antigenic targets of toxin components which correlate with protection. Baboon samples from the Kurosawa Technical Project before and after vaccination, toxin challenge and spore challenge will allow further definition of the minimal necessary protective response and evaluation of the temporal evolution of anthrax specific B and T cell responses. In collaboration with the Wilson Technical Project we will test and characterize fully human neutralizing monoclonal antibodies generated after AVA vaccination. Other work focuses on understanding clinical and cellular correlates of protection after AVA vaccination. This project will provide understanding of the key aspects of protective immune responses to anthrax toxins and allow generation of better vaccines, immunotherapeutics and rapid screening tests for detection.